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Discussion Starter #1
I've got an L92 engine, stock, except for a Tilden oil pan. ~65k miles supposedly. I've been chasing a bad oil leak near the back of the pan, which I thought was the pan gasket. I got a stud set, and installed a new gasket with tons of RTV, and no change to the leak.

After running mid RPMs for a 20 minutes, it leaks 3-4 drops per second! Leak is coming directly from the back of the engine, I'm suspecting rear main.

After doing some reading online, I wonder if my crankcase is getting pressurized. I've removed the PCV, and an running a straight vent from the driver valve cover with a 3/8 fuel line that goes around the front and bottom of the engine and then to a catch can with a 1/4" open port. This is the same setup I ran on a gen 2 vortec for years with no issues.

Engine runs great, tons of power, and does not burn oil. Is this vent sufficient? Do I need an actual vacuum to help remove pressure?
 

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On my '99 5.3 I run a vent like you describe. Hose from drivers side around motor to catch can. No issues.
 

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I have an LY6 and run one 3/8 hose on each valve cover, three sides and down, no catch can, no issues. My old buggy with an LQ4 had the valve covers T'ed to a single hose, then to one of those speedway catch cans with the 1/4" nipples. That used to blow oil out of the dipstick.
 

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I've got an L92 engine, stock, except for a Tilden oil pan. ~65k miles supposedly. I've been chasing a bad oil leak near the back of the pan, which I thought was the pan gasket. I got a stud set, and installed a new gasket with tons of RTV, and no change to the leak.

After running mid RPMs for a 20 minutes, it leaks 3-4 drops per second! Leak is coming directly from the back of the engine, I'm suspecting rear main.

After doing some reading online, I wonder if my crankcase is getting pressurized. I've removed the PCV, and an running a straight vent from the driver valve cover with a 3/8 fuel line that goes around the front and bottom of the engine and then to a catch can with a 1/4" open port. This is the same setup I ran on a gen 2 vortec for years with no issues.

Engine runs great, tons of power, and does not burn oil. Is this vent sufficient? Do I need an actual vacuum to help remove pressure?
I sure hope your pan doesnt have weld porosity like mine did. I have a PAC FAB pro pan (just a Tilden with a skid on it) and I chased my leak down to a shit weld on their expensive ass pan. I’ll never buy anything from them again.
 

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I sure hope your pan doesnt have weld porosity like mine did. I have a PAC FAB pro pan (just a Tilden with a skid on it) and I chased my leak down to a shit weld on their expensive ass pan. I’ll never buy anything from them again.
We're fighting one at work, an LQ4 with the same leak issue, leaks from the rear, and it also has a Tilden pan. The pan is definitely not flat. I'm not sure if that's by design or not. We were told to use their stud kit and that would fix it. Of course it still leaks. We will have to look at welds the next time it is off. I've been trying to argue to put the stock pan back on.

Kevin
 

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might not be the rear main, isn't there a cam cover or galley plug behind flywheel that has been known to leak on the LS's ??
 

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Discussion Starter #10
I messed with this a bit today. Took the oil fill call off and let it idle for 30 minutes. Only leaked about 3 drops in that time. Put the cap back on, starting leaking heavily right away ( >1 drop/sec). Took the cap off, and it popped out in my hand. There was obviously pressure building in the crankcase. Took the hose that was on the driver valve cover vent off. Air was obviously coming out, but with the oil cap on, the leak continued. Take the cap off, and the leak quickly stops (almost).

I'm going to do a leak down test to see if the rings are blowing by, but I'd be surprised if that was it. This is a stock engine with low miles.

Does the crankcase require a vacuum from the intake to help evacuate pressure? Reading on the internet is inconclusive. People are saying both things.
 

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It doesn't need engine vacuum to vent. I typically just vent to atmosphere though a catch can.If you feel air coming out when you pull the fill cap off you have an internal issue. Stuck rings or cracked piston.
My 6.0 did that when I broke a piston.
 

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certainly doesn't require vacuum at idle. i'd also suspect an internal issue, though it may run fine for a long time (another 100k miles) like that if you can get the oil leak resolved

the crankcase has several stock drains/vents between the case and the heads and really shouldn't much to vent to atmosphere, so you are getting more crank pressure than the drain ports can flow to the head and more than your vent line can flow. not normal for flat idle

lsx oil pans for more reading
 

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Leaving this info here, I had the opposite issue, was running PCV and had a squealing sound at idle, couldn’t figure it out, finally found out it had too much vacuum and was pulling on the seal or running it dryer and it would squeal, test was as simple as remove PCV and the case vented = no squeal, put it back in and build vacuum and it would squeal. Now I run dual 3/8” to 1/2” vent line no catch.
 

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I'd say a catch can is your biggest friend for any LS especially if it's a Gen 4. My wife's l92 in her 2008 Yukon Denali just had to be rebuilt because the oil was puddling in the intake and wiped out the rings. Engine had just under a hundred thousand miles on it oh, I bought it with 85000 miles and it had to be bored out to 4.080. My machine shop said it's the most they have ever had to but an aluminum LS block.

I'd have to do some digging to find all the GM technical bulletins again, but their acceptable loss is one quart every 2000 miles on a Gen 4 l92.

The rebuild is getting a nice elite engineering dual catch can. Plus she complained it was slow off the line so I'm throwing in a Comp Cams VVT cam, long tube headers and rebuilt the 6l80 with kolene steels, red clutches and all the sonnax/transgo updates.
 

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i was told by CBM that each side needs a -8 breather min
 

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might be worth putting a wire mesh screen on the cap side to filter out some oil if you notice 'excessive' oil coming out the 5/8 hose :beer:
 

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As a bandaid, I ordered a oil cap with a -10 fitting on it. Going to plug it to a 5/8 hose and run it this afternoon.
did that help with it oushing out past the seals?
 

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Discussion Starter #19
did that help with it oushing out past the seals?
Yes, significantly. Went on a run on Sunday. Hardly noticed any leakage during the run. (1-2 drops when stopped). When parked, there were probably 5-6 drops overnight.
Before it was 1-2 drops per second (continuously) when running, and a good size puddle overnight.

Not perfect, but a decent bandaid.
 
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